1. Field of the Invention
The present invention relates to a technology for determining life of a photoreceptor in an image forming apparatus.
2. Description of the Related Art
Conventionally, there has been a type of image forming apparatus that electrostatically forms an electrostatic latent image on a surface of a photoreceptor, develops the latent image by toner, and a toner image is transferred to a recording medium such as paper and is fixed thereon, thereby forming a printed matter. In this type of image forming apparatus, a photoreceptor layer on a surface of a photoreceptor can be worn due to frictions by a developer on a cleaning blade or in a developing nip, or can fatigue due to repetitions of charging and neutralization. Therefore, the photoreceptor needs to be replaced regularly according to the service life of thereof.
Types of photoreceptors used in an image forming apparatus include a selenium photoreceptor, an amorphous silicone photoreceptor, and an organic photoreceptor. The selenium photoreceptor and the amorphous silicone photoreceptor have an advantage in that they have a longer service life because of high surface hardness and scrape resistance. However, the selenium photoreceptor needs to be collected after use because of environmental consideration or the like, and thus it is used only in a part of high-speed machines. The amorphous silicone photoreceptor has a lower surface resistance than other types of photoreceptors, and particularly, the amorphous silicone photoreceptor has a disadvantage in that an electrostatic latent image is disturbed in a high-temperature and constant-humidity environment, and this can cause a phenomenon referred to as “image deletion”. Further, in the amorphous silicone photoreceptor, the rate of dark decay is very high as compared to other types of photoreceptors because of the low surface resistance, and a charge potential is not stable in a developing unit away from a charging unit (with a time passed since being charged), because temperature dependency of the rate of dark decay is very large. From these reasons, the amorphous silicone photoreceptor is generally mounted with a heater to control its temperature to be constant by detecting the temperature thereof. Further, to reduce cost, there has been proposed a method of temperature detection of a photoreceptor to control the charge potential of the photoreceptor and development bias according to the detected temperature, without performing temperature control of the photoreceptor by a heater (for example, see Japanese Patent Application Laid-open No. H9-185218 and Japanese Patent Application Laid-open No. H11-109688). Meanwhile, the organic photoreceptor has been most widespread because of a reasonable production cost; however, the organic photoreceptor has a disadvantage in that it is easily scraped due to low surface hardness, and thus its service life is short. Therefore, when an organic photoreceptor is used, it is very important to accurately determine the service life thereof. The temperature dependency of the organic photoreceptor is very low as compared to that of the amorphous silicone photoreceptor, and thus, conventionally, with regard to detection of the temperature of the organic photoreceptor and prediction of the service life thereof, the temperature of the organic photoreceptor itself has not been focused.
Conventionally, endurance tests or the like are performed beforehand in a standard environment and use condition to obtain the number of prints and cumulative number of revolutions of a photoreceptor until it reaches the end of the service life, and the service life is set based on the results of the tests. However, because the service life of the photoreceptor largely depends on a use environment and use condition of an image forming apparatus that uses the photoreceptor, it is difficult to accurately predict the service life. Therefore, in practice, before reaching the number of prints set as a preset service life, printed matters having a considerable defect in quality may be output, or replacement of the photoreceptor may be performed although it is still sufficiently useful.
Therefore, a method of detecting a fatigue state of a photoreceptor to determine the service life thereof based on its detection result has been proposed. For example, as a method of detecting a fatigue state of a photoreceptor, there has been proposed a method of detecting a surface potential of a photoreceptor to determine the service life thereof based on its detection result. For example, Japanese Patent Application Laid-open No. H9-190120 discloses a method of determining the service life of a photoreceptor by comparing a detected saturated potential and a residual potential to a preset potential value. Japanese Patent Application Laid-open No. 2006-139272 discloses a method of determining the service life of a photoreceptor according to a difference between a charge potential and a residual potential.
However, in the methods disclosed in Japanese Patent Application Laid-open No. H9-190120 and Japanese Patent Application Laid-open No. 2006-139272, the service life is determined by a measured residual potential itself, and the temperature dependency of a residual potential of an organic photoreceptor is not taken into consideration. In these methods, determination of the service life of the photoreceptor is performed according to mixed information elements including a change in the residual potential due to deterioration of the photoreceptor and a change in the residual potential due to a temperature change of the photoreceptor. Therefore, there is no accuracy in determining the service life, and the determination can be erroneous in some cases. Particularly, in a case that immediately after an apparatus is switched on in the winter season where an external temperature is low, the temperature of the photoreceptor is low and the residual potential becomes very high, and thus the service life of the photoreceptor can be detected erroneously.